The term ‘colour element’ is used herein to refer to a display component from which coloured light is emitted, transmitted, reflected or scattered when the display is suitably activated. The term includes light filters which absorb certain wavelengths of light, and other components such as wavelength-sensitive reflectors or scatterers, and fluorescent or phosphorescent materials. Commonly, the colour elements are light filters which are part of a colour filter matrix. Displays employing phosphorescent colour elements are described in U.S. Pat. No. 4,830,469 and U.S. Pat. No. 5,608,554.
The colour element matrix is one of the most expensive components in a lightvalve-type backlit display, for example a liquid crystal polarisation switch mode display. The colour element must be physically close to the electro-optic switching layer to avoid colour parallax, and must be aligned with at least the ‘column’ electrode patterning in the case of RGB colour stripes. Difficulties in achieving this alignment add to manufacturing costs.
A known production process involves patterning the colour matrix onto the final display substrate, planarising the matrix, and then forming the display cell. While this minimises the distance between the electro-optic switch and the colour filter element, it is very expensive and requires multiple lithographic steps.
A method of forming electrode patterns for a passively-addressed alphanumeric liquid crystal display (LCD) is described in U.S. Pat. No. 3,902,790. The method involves providing gold-plated stripes for busbars and other conductive elements which are in areas where characters are not displayed, to provide highly conductive paths between display characters. Methods of forming colour filters for LCDs by ink jet printing in pre-defined channels are described in JP 2003035814, JP 11142641, U.S. Pat. No. 5,552,192 and U.S. Pat. No. 5,576,070. Busbars are also used to address other types of displays, for example active matrix LCDs, in which operation of each pixel is controlled by a corresponding thin film transistor (TFT).